Multi-screw extruder technology has established itself in recent years. Primarily extruders with several screws arranged in a ring or circle, which all each mesh with two adjacent screws, e.g., the 12-screw RingExtruder®, are characterized by particularly high throughputs and narrow retention time spectra. Bulk materials with a high apparent density, e.g., granules, are particularly advantageous for molding.
However, when the objective is to mold loose bulk material with a relatively low apparent density (approx. 20 to 60% of solids density), e.g., flocs or macerate, in such a multi-screw extruder, the problem becomes that the extruder feed opening is only able to draw in bulk material arriving in a loose bed with a high content of air with a low throughput at the feed opening. Means common in prior art, such as stuffing screws at the feed opening and/or degassing the extruder casing directly on the side opposite the conveying part of the feed opening, provide only an unsatisfactory solution. Therefore, these multi-screw extruders, which in themselves offer a very high throughput, are always “underfed” in the case of loose bulk material, e.g., polyethylene terephthalate (PET) flocs, which stem primarily from recycled bottles (RPET). Their feed opening is operationally limited for such loose bulk material.